While few users need 64GB, breaking the 16GB barrier for the quad-core model is/was a big deal, extending the range of file sizes and software that are viable on the quad-core machine. This is especially interesting, because as this was written, the quad-core 3.33GHz Mac Pro remained the fastest Mac Pro available for most uses.

The 8GB option is viable for some users, but not recommended for serious work with photography.

The 12GB is the magic number for most users, a no-brainer. But users working regularly with big files should be thinking about 16GB or 24GB or even 32GB. See Optimizing Photoshop and Optimizing Lightroom.

OWC 8GB memory modules

RAM Disk

With 32GB or 64GB memory, some users might find a RAM disk useful for specific applications.

While Photoshop CS4 is still a 32-bit program, only able to access ~3GB of memory directly, working with huge files benefits immensely from gobs of extra memory, because Mac OS X uses extra memory for caching writes/reads to and from the drive eg the Photoshop scratch volume.

At the end of the diglloydHuge tes using 64GB of memory, I observed that Mac OS X had used 48GB of memory for caching, which explains the speed improvement; the test generates a monster 56GB scratch file.

All modules worked flawlessly. I was even able to mix OWC modules of 8GB and 4GB sizes, though that is largely pointless.

Mixing 4GB and 8GB modules worked OK (but not recommended)

Memory bandwidth

As part of MemoryTester’s output, the memcpy() speed is shown, thus revealing how fast the memory is. This is of little importance with real applications, but can matter by a few percent in certain memory-intensive computations.

Memory bandwidth is fastest with 3 or 6 modules, because of triple-channel memory in the Mac Pro. Triple channel memory is not (as theory advises) 50% faster when moving memory via memcpy(); it is only about 28-36% faster. That’s the Real World.

Memory bandwidth testing is subject to the vagaries of where the system actually allocates the memory, how threads are scheduled, how many threads are created, whether hyperthreading is used, etc. These figures are not memory bandwidth per so much as what a real program can actually do on Mac OS X 10.6.2.

Stress test

There is nothing that can stress you Mac more; MemoryTester keeps all CPU cores at 100% while relentlessly writing and reading memory (disk I/O on all disks is optional). Without a doubt, 99.99% of Mac Pro users will never stress their machines this hard! The stress test generates maximum heat, the killer of marginal components, and a sure way to cause system crashes with “weak” parts.

During and after the stress test, be sure to check for ECC errors. I recommend a minimum test duration of one hour, but 3-4 hours or even overnight will prove beyond a doubt that things are rock-solid.

I experienced no ECC errors with the 8GB modules on either of my Mac Pro systems: perfect!

A fully “stressed” Mac Pro with 64GB — click for larger image

In use

I worked with the 8GB modules over the course of a week with all my usual software. Flawlessly operation, just as with the 4GB modules I had been using.

Why do 8GB module cost more?

Ideally, an 8GB module would be only twice the price of a 4GB module. But the 8GB modules use the latest high-density memory chips. These are more costly parts, and hence the modules are more expensive to build. Over time prices should decline.

If you don’t need to max-out your Mac Pro right now, stick with 4GB memory modules and go to 12GB or 16GB in your quad-core (or 24GB in your 8-core). In the 8-core machine, you could also go to 12GB as six 2GB modules, your least costly option.

Do you need more memory?

Determine if you need more memory by using Activity Monitor to see what’s happening while using your favorite programs.

OWC test lab

Click to read about the OWC test lab

OWC maintains a testing lab with every Mac they selling memory for, so they can guarantee it works in your Mac.

Conclusions

The arrival of 8GB modules is a boon to quad-core Mac Pro users, extending the lifespan and versatility of the machine at a time when 64-bit Mac OS X Snow Leopard is gaining traction, and programs are making the transition to 64-bit capability. More memory will become more and more useful.

Note well that even today’s 32-bit Photoshop CS4 still benefits from much as much as 64GB memory for large files.